A semiconductor module which is configured from an IGBT or MOS-FET that controls current switching is a principal constituent component of power conversion devices, such as inverters and chargers. With the advance of electric powered vehicles, there are demands for increased output from power conversion devices, and the current capacity of semiconductor modules is tending to increase.
Moreover, with advances of the semiconductor elements made of SiC, and the like, operation has become possible in high-temperature environments around 200° C. However, the structural reliability required in the cooling and heating cycle, etc. is much stricter than in the prior art. Therefore, semiconductor modules are required to both increase current capacity through higher output, and ensure reliability enabling normal operation over a long period of time in a high-temperature environment.
In order to increase the current capacity, it is essential to reduce the electrical resistance of the conducting members. Moreover, in order to ensure reliability from low-temperature to high-temperature environments, it is imperative to reduce the thermal stress in the junctions of the constituent members inside the semiconductor module, and to reduce the residual stress in these junctions.
In a conventional semiconductor module, in order to increase the current capacity, the electrodes of the semiconductor element and the bus bar constituting the main terminal are joined directly (see, for example, PTL 1).